Ok, I've seen both Piranha 3D and The Expendables, and I had to agree with him that Pirnaha 3D was the better film. Yes, it was cheese, but it was good cheese as it kind of harkened back to the b-movie monster flicks of yesteryear (specifically the Roger Corman-produced/Joe Dante-helmed original Piranha).
Bob's somewhat adolescent assertions as to why it was good aside, the difference between The Expendables and Piranha 3D was because Piranha 3D 1) Had better cinematography when it came to the action scenes, eschewing the shakycam editing that seems to plague most modern action movies these days (and seems to be a crutch for lazy directors and cinematographers who don't want to seem to go to the trouble of having to choreograph a fight scene) and more importantly 2) unlike The Expendables, it does not even try to take itself seriously. It knows the premise itself is ludicrous, is not afraid to admit it, and even embraces it and runs with it full-tilt gonzo. Contrast this with The Expendables, which tries to make some sort of pretense or justification for all its action scenes. To wit, the scene with Rourke and Stallone where Rourke makes a speech about saving what's left of his soul or something or other, with the implication that Stallone's character is having a crisis of conscience and decided to do it for his own sake. Yet the plot only pays it lip service. Had this idea been more fleshed-out, I think The Expendables would have had more dramatic weight to it and the fight scenes would have actually meant something. But in the end all we got were a bunch of meaningless explosions.
But I do agree that Bob missed the point why everyone was so angry with him, as has been pointed out, it was because of his implied insults to those who went to see The Expendables. His liking Piranha 3D may on the surface make him look like a hypocrite, but I think his arguments here over why Piranha 3D was the better B-movie speak for themselves.
(BTW, the two movies are linked in another interesting way, as Kelly Brook once dated Jason Statham for awhile. Think that one over.)
As for Centurion, that one kind of snuck up on me. Apparently either it wasn't released in my area or is going to be available on On Demand. Either way, I'll need to check it out as I've loved all of Neil Marshall's films (especially Dog Soldiers) and he hasn't steered me wrong yet.